From the earliest development of radar military
sky-watchers were puzzled by mysterious echoes on their screens. In the
second in his series on secret files released at Britain’s National
Archives, DAVID CLARKE reveals how Britain’s scientists struggled
to explain these “radar angels.”

During the 1930s the Air Ministry secretly built a chain
of radar stations along the eastern coastline of England that was to provide
a crude but effective early warning system against air raids. In 1940
during the Battle of Britain this “secret weapon” gave the
RAF a crucial tactical advantage over the superior strength of the Luftwaffe.
But although at this time British radar was the most advanced in the world,
it was far from foolproof, as was demonstrated by a series of strange
incidents the following year.

Late on the night of 20 March 1941, while the threat
of German invasion remained, RAF Fighter Command was placed on red alert
when its radar chain reported an attack on Britain’s south coast.
Up to five separate stations could “see” a massive formation
of blips moving slowly across the channel precisely as would be expected
if a massive night raid by German bombers was imminent. As tension grew
the blips approached from the direction of the Cherbourg peninsula in
France until within 40 miles of the Dorset coast. At RAF Worth they lingered
on the radar picture for two hours and appeared to change from massed
groups to single echoes which then faded out.

The next night the blips were back and engineers were called in to make
adjustments that might eliminate “noise” from the system.
For a period of weeks stations continued to report both mass formations
and individual echoes. Whilst sceptical, senior officers began to fear
these could be part of a sophisticated German plot to jam British radar
with false signals as aircraft or towed gliders prepared for a real invasion.
RAF fighters directed by ground radar were ordered to intercept and shoot
down the mysterious objects. But when they arrived at the spot in the
English Channel where the echoes were visible on radar, nothing could
be seen.

Recalling this incident sixty years later Sir Edward
Fennessey, who was responsible for the radar chain, recalled that no explanation
was ever found “and because we were busy fighting a war we spent
no time investigating this phenomena.” Afterwards he retold the
story at a dinner party where he entertained guests with his theory that
the echoes were really guardian angels, “the souls of British soldiers
killed in France over the centuries returning to defend their country.”

Although it was intended as a joke Sir Edward’s
fantasy caught the imagination of serving airmen who were watching “ghosts”
on their radar screens. According to the Oxford English Dictionary, from
1947 the term “angels” was commonly used to describe “unexplainable
echoes” seen not only on radar pictures in Britain, but across the
world. Since the war angels had been reported on a variety of ground radars
operating on the short 10cm and 25cm wavelengths. According to one source
they often completely covered the screen and “appeared as a cloud
of responses very similar to the echoes obtained by small aircraft”
precisely as they had in 1941. When they appeared as an individual echo
they could easily be mistaken for a fighter-type aircraft as they followed
a steady course and were plotted at heights from 2- 10,000 feet.

Angels continued to be seen in the 1950s after the arrival
of MTI (moving target indicator) radars, which were meant to eliminate
much of the “noise” and ground clutter that plagued early
systems. By 1954, when powerful Type 80 radars were installed at the radar
research station in Malvern, angels had become a considerable hazard for
fighter controllers. Type 80 had far greater range and performance than
the wartime radar but was still plagued by angels. On some occasions they
polluted radar screens to such an extent that they interfered with RAF
exercises. At that time no one had a satisfying explanation for the phenomenon
but there were two competing theories. The first was that angels were
caused by temperature inversions in the lower atmosphere that created
pockets of air which reflected radar beams. But this could not fully account
for how the echoes moved against the prevailing winds or in excess of
measured wind speeds.

The second theory was that angels were really formations
of birds flying to and from their breeding grounds as part of their annual
migrations. But ornithologists who were using radar to study bird migrations
had a very difficult time persuading the RAF to take this theory seriously.
Top brass were loath to admit that creatures as small as birds were capable
of disrupting their operations. Events were soon to prove how wrong they
were. When inquiries were made, a mass of anecdotal testimony from radar
staff came to light that supported the bird theory. During the war staff
at coastal radar stations had even correlated “angels” on
their screens with flights of seabirds spotted with the naked eye. On
rare occasions large individual birds could cause more chaos. Barry Huddart,
who was posted at HQ Fighter Command in 1957, recalled one incident “when
fighters were scrambled to intercept an echo on a radar screen which turned
out to be a Golden Eagle at 25,000 ft in a jet stream, very unusual but
nonetheless true.”»

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